I have a Denon AVR-1708 and find that a Sony SA-W305 Active Superwoofer that works on a less expensive combo-system won't work when connected to the subwoofer pre-out connector on the Denon AVR. I am non technical. The device is rated at 50 watts per channel RMS power (Canada). It says 6 ohms, DIN for the version sold for Europe but doesn't specify for Canada. Any comments would be appreciated.